There's Sombreria Mil on the Carrer de Fontanella, they have been around forever: http://www.sombrereriamil.com/
I am sure @Kuki will be able to help you more, she lives in Barcelona.
By the way, did you google it or have you been there @Celia? Is there anything you don't know?! You always impress me with your hatty knowledge!
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